Oxygen gas concentrator with outlet accumulator

ABSTRACT

An oxygen concentrator comprises a product tank that is fluidly coupled to at least one sieve bed, and a product gas accumulator tank that is fluidly coupled to the product tank via a first conduit and to an outlet port via a second conduit, wherein the first conduit and the second conduit are disposed to allow at least a portion of product gas to flow from the product tank to the outlet port.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationtitled “OXYGEN GAS CONCENTRATOR WITH OUTLET ACCUMULATOR,” filed on May23, 2017, and having Ser. No. 15/603,380, which claims priority benefitof the U.S. Provisional Patent Application titled, “Addition of anOutlet Accumulator to a High Pressure Concentrator to allow Use ofeither a Ventilator or Nasal Cannula,” filed on May 24, 2016 and havingSer. No. 62/341,021. The subject matter of these related applicationsare hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to medical devices and, morespecifically, to an oxygen gas concentrator with an outlet accumulator.

Description of the Related Art

Oxygen therapy is the standard of care for many patients with lungdiseases in the early to mid-stages. In particular, individuals withChronic Obstructive Pulmonary Disease (COPD), the third leading cause ofdeath in the United States, are prescribed with oxygen therapy toincrease blood oxygen saturation. In many cases, patients with COPD canalso benefit from improved ventilation of the lungs to help evacuateelevated levels of carbon dioxide. However, because of the high cost andlarge sizes of traditional mechanical ventilators, such patients aregenerally not prescribed ventilation therapy until hospitalized or inthe late stages of the disease even though ventilation therapy, andventilation with oxygen therapy have all proven to be beneficialtherapies for patients with COPD (with increasing benefit,respectfully). Consequently, the use of oxygen concentrators inconjunction with mechanical ventilators has been studied as a means toreduce the cost of ventilation with oxygen therapy.

However, oxygen concentrators are generally not well-suited for directcoupling with mechanical ventilators. Specifically, ventilatorsgenerally require a gas source that can provide a spontaneous flow rateof more than 100 liters per minute (LPM) to provide adequate ventilationtherapy during an inspiratory effort, while a typical oxygenconcentrator can deliver a continuous flow rate on the order of onlyabout 1 to 10 LPM. Accordingly, a conventional oxygen concentrator isgenerally incapable of meeting the large spontaneous flow raterequirements of a typical ventilator that is being used to assist theinspiratory efforts of a patient. Among other things, depletion of theproduct tank in the oxygen concentrator can occur. Product tankdepletion, in which the product gas pressure in the product tank fallsbelow a target minimum target pressure, reduces the expected flow rateof product gas delivered to the ventilator, which is highly undesirable.

To prevent product tank depletion when an oxygen concentrator is used inconjunction with a ventilator, the operating pressure of the producttank can be elevated. With the higher product tank pressure, moreproduct gas is available for each inspiratory effort of the patient.However, higher product tank pressure puts significantly greater demandon the oxygen concentrator compressor, resulting in more heatdissipation and noise, increased energy expenditure, and reducedcompressor life.

Alternatively, the product tank of the oxygen concentrator can beincreased in size such that more product gas is available for eachinspiratory effort of the patient. However, a larger product tankgenerally results in an oxygen concentrator that is heavier and moreexpensive than a conventional oxygen concentrator. Furthermore, whilethe increased size of the product tank theoretically makes more productgas available for each inspiratory effort of the patient, in practicethe pressure drop in the system between the product tank and theconcentrator outlet prevents the added capacity of the product tank frommaintaining a constant outlet pressure throughout a patient'sinspiratory efforts.

As the foregoing illustrates, what is needed in the art are moreeffective ways to interface oxygen concentrators with mechanicalventilators.

SUMMARY OF THE INVENTION

One embodiment of the present invention sets forth an oxygenconcentrator that is configured for use in conjunction with a mechanicalventilator. The oxygen concentrator includes a product tank that isfluidly coupled to at least one sieve bed, and a product gas accumulatortank that is fluidly coupled to the product tank via a first conduit andto an outlet port via a second conduit, wherein the first conduit andthe second conduit are disposed to allow at least a portion of productgas to flow from the product tank to the outlet port passes through theaccumulator tank.

At least one advantage of the disclosed design is that an oxygenconcentrator can be connected to a mechanical ventilator and provide amore constant flow of product gas to the mechanical ventilator relativeto prior art designs.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1A is a block diagram of an oxygen-ventilation therapy system,according to various embodiments of the present invention.

FIG. 1B is a block diagram of an oxygen therapy system, according tovarious other embodiments of the present invention.

FIG. 2 is a more detailed schematic illustration of the oxygenconcentrator of FIGS. 1A and 1B, according to various embodiments of thepresent invention.

FIG. 3 is a graph illustrating pressure at various locations within aconventional oxygen concentrator of FIG. 1B when the oxygen concentratoris fluidly coupled to the ambient pressure delivery device of FIG. 1B,according to various embodiments of the invention.

FIG. 4 is a graph illustrating pressure at various locations within aconventional oxygen concentrator as the conventional oxygen concentratorprovides an intermittent volume of oxygen-enriched gas to a respiratoryventilation device.

FIG. 5 is a graph illustrating pressure at various locations within theoxygen concentrator of FIG. 2 as the oxygen concentrator provides anintermittent volume of oxygen-enriched gas to a respiratory ventilationdevice, according to various embodiments of the invention.

FIG. 6 is a graph illustrating pressure at various locations within theoxygen concentrator of FIG. 2 as oxygen concentrator provides a constantflow of oxygen-enriched gas to an ambient pressure delivery device,according to various embodiments of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a more thorough understanding of the embodiments of the presentinvention. However, it will be apparent to one of skill in the art thatthe embodiments of the present invention may be practiced without one ormore of these specific details.

Stationary and portable oxygen concentrators commonly employ a processcalled pressure swing adsorption (PSA) to increase the oxygenconcentration of the incoming ambient air before the air is delivered toa patient. Generally, the delivered oxygen concentration is between 90and 96%, due to concentrator efficiencies and remaining constituentelements in the air that are not adsorbed in the process. Stationary andmost portable oxygen concentrators use the PSA process to deliver aconstant flow of oxygen to the patient, typically 1 to 5 LPM, and insome cases up to 10 LPM

As noted above, the continuous flow rate of oxygen concentrators isgenerally too low to serve as a sole gas source for conventionalmechanical ventilators: typical ventilators require a source of supplygas that can provide a flow rate of about 100 LPM to provide adequateventilation therapy during an inhalation. However, ventilators thatutilize entrainment technology only require approximately 20 LPM of flowfrom the ventilator gas source during an inhalation to provide 100 LPMof ventilation support. For a spontaneous intermittent ventilator, theaverage delivered volume from the gas source (minute volume) is based onthe flow during inhalation, the inhalation delivery period and thepatient's breath rate. The source gas minute volume requirements of aventilator that utilizes entrainment technology typically ranges from 1to 5 LPM, which is well within the continuous flow rate provided by moststationary oxygen concentrators.

According to embodiments of the invention, the output of an oxygenconcentrator, i.e., oxygen-enriched product gas, is fluidly connected toa respiratory ventilation device, thereby facilitating oxygen andventilation therapy. Furthermore, to meet and maintain a targetedoperating oxygen flow for the respiratory ventilation device, the oxygenconcentrator includes an accumulator tank that is disposed at or near anoutlet port of the oxygen concentrator. The accumulator tank isconfigured to prevent product tank depletion in the oxygen concentratorduring the high product gas demand from the respiratory ventilationdevice that occurs during each patient inspiratory effort, therebyensuring that product gas is supplied to the respiratory ventilationdevice at a consistent flow rate. Specifically, the accumulator tank isconfigured to temporarily store product gas between each patientinspiratory effort and to supply the stored product gas at a consistentflow rate during each patient inspiratory effort. As a result, pressureswings in the product tank of the oxygen concentrator are reduced inresponse to product gas demand from the respiratory ventilation device,and product tank depletion is prevented.

FIG. 1A is a block diagram of an oxygen-ventilation therapy system 100,according to various embodiments of the present invention.Oxygen-ventilation therapy system 100 is configured to simultaneouslyprovide both oxygen therapy and ventilation therapy to a patient 101,and includes a respiratory ventilation device 120 and an oxygenconcentrator 130. As shown, an output 131 of oxygen concentrator 130 isfluidly coupled to an inlet 121 of respiratory ventilation device 120,so that respiratory ventilation device 120 provides oxygen-enrichedinhalation gas 123 to patient 101 during ventilation therapy.

Respiratory ventilation device 120 may be any technically feasiblerespiratory ventilator capable of moving breathable air into the lungsof patient 101. Thus, respiratory ventilation device 120 facilitates thebreathing of patient 101, who may be physically unable to breathe, ormay be breathing insufficiently. Inhalation gas 123 may be deliveredfrom respiratory ventilation device 120 to patient 101 by a nasal mask,nasal cannula, intubation, or the like.

In some embodiments, respiratory ventilation device 120 is configured toemploy entrainment of ambient air in the delivery of inhalation gas 123to patient 101. In such embodiments, respiratory ventilation device 120directly provides a source gas 122 that is only a portion of theinhalation gas 123 inhaled by patient 101. The remaining portion ofinhalation gas 123 is ambient air 124, which has been entrained bysource gas 122. In general, source gas 122 is typically a relativelysmall portion of inhalation gas 123, for example between about 10% to50% of inhalation gas 123. Thus, when the instantaneous flow raterequirement for respiratory ventilation device 120 during an inhalationby patient 101 is, for example, 100 LPM, the instantaneous flow raterequirement for inhalation gas 123 is also 100 LPM, while theinstantaneous flow rate requirement for source gas 122 is only about 10to 30 LPM. In such embodiments, most or all of source gas 122 may beprovided by oxygen concentrator 130 as an oxygen-enriched product gas132. Alternatively, source gas 122 may include a combination of anoxygen-enriched product gas 132 and ambient air that is mixed withoxygen-enriched product gas 132.

Oxygen concentrator 130 is configured to produce oxygen-enriched productgas 132 for providing oxygen therapy to patient 101. Thus, patient 101receives both ventilation therapy via respiratory ventilation device 120and oxygen therapy. According to various embodiments, oxygenconcentrator 130 may employ any technically feasible oxygenconcentration process for providing oxygen-enriched product gas 132. Forexample, oxygen concentrator 130 may be configured to employ a pressureswing adsorption (PSA) process, a rapid pressure swing adsorption (RPSA)process, a vacuum pressure swing adsorption (VPSA), or any otherderivative process thereof. In each case, oxygen concentrator 130 isconfigured to provide a targeted flow rate of product gas 132 for eachinspiratory effort of patient 101. To that end, 130 is configured withan accumulator tank, as described below in conjunction with FIG. 2.

In some embodiments, oxygen concentrator 130 is configured as aconventional semi-portable (wheeled) or non-portable (stationary) oxygenconcentrator, for example for use in a home or hospital setting. Inother embodiments, oxygen concentrator 130 is a portable oxygenconcentrator, such as a device configured to be carried in a backpack.In such embodiments, respiratory ventilation device 120 may also beconfigured as a portable or ultra-portable device.

FIG. 1B is a block diagram of an oxygen therapy system 150, according tovarious other embodiments of the present invention. Oxygen therapysystem 150 is configured to provide oxygen therapy to a patient 101without ventilation therapy, and includes oxygen concentrator 130. Asshown, output 131 of oxygen concentrator 130 is fluidly coupled to anambient pressure delivery device 140, such as a nasal cannula, a nasalmask, or any other device configured to deliver supplemental oxygen topatient 101 at ambient pressure. During operation oxygen therapy system150 supplies oxygen-enriched product gas 132 directly to patient 101 viaa continuous flow of oxygen-enriched product gas 132 via ambientpressure delivery device 140.

FIG. 2 is a more detailed schematic illustration of oxygen concentrator130, according to various embodiments of the present invention. As notedabove, oxygen concentrator 130 is configured to produce anoxygen-enriched product gas to a patient who is receivingoxygen-ventilation therapy via oxygen-ventilation therapy system 100 orwho is receiving oxygen therapy via oxygen therapy system 150. As such,oxygen concentrator 130 includes, without limitation, a product gasgeneration stage 210, a product gas supply stage 240, and a controller250. Product gas generation state 210 is configured to generate aproduct gas, such as oxygen-enriched product gas 132, and product gassupply stage 240 is configured to store and supply the product gas topatient 101, either via respiratory ventilation device 120 or ambientpressure delivery device 140.

In the embodiment of oxygen concentrator 130 illustrated in FIG. 2,product gas generation stage 210 includes, without limitation, an inletfilter 201, a pump 202, and, in some embodiments, a vacuum pump 203, allconnected via pneumatic plumbing 204, as shown in FIG. 2. Product gasgeneration stage 210 further includes, without limitation, a first sievebed 221 and a second sieve bed 222, fluidly connected to each other byan equalization orifice 223. First sieve bed 221 and second sieve bed222 are each configured to remove nitrogen from air present therein, sothat product gas exiting first sieve bed 221 or second sieve bed 222 isan oxygen-enriched gas. Typically, first sieve bed 221 and second sievebed 222 each include a nitrogen-adsorbing material, such as anitrogen-adsorbing zeolite. Consequently, as air flows into one of firstsieve bed 221 or second sieve bed 222, the air passes through thenitrogen-adsorbing material, a significant portion of the nitrogen isadsorbed, and the remaining gas in the sieve bed is primarily oxygen.This oxygen-enriched gas can then flow into a product tank 249.

Product gas generation stage 210 further includes, without limitation, afirst sieve bed fill valve 231 coupled to an inlet of first sieve bed221, a first sieve bed dump valve 232 fluidly coupled to an outlet offirst sieve bed 221, a second sieve bed fill valve 233 coupled to aninlet of second sieve bed 222, and a second sieve bed dump valve 234fluidly coupled to an outlet of second sieve bed 222. First sieve bedfill valve 231 is a controllable valve that selectively allows entry ofair or any other suitable gas to enter first sieve bed 221. First sievebed dump valve 232 is a controllable valve that selectively allows gaspresent in first sieve bed 221 to exit first sieve bed 221 when at ahigher pressure than ambient. Second sieve bed fill valve 233 and secondsieve bed dump valve 234 operate similarly with respect to second sievebed 222.

In the embodiment of oxygen concentrator 130 illustrated in FIG. 2,product gas supply stage 240 generally includes, without limitation,product tank 249, which is fluidly connected to first sieve bed 221 andsecond sieve bed 222, a first check valve 235, and a second check valve236. First check valve 235 is disposed between first sieve bed 221 andproduct tank 249 and is configured to prevent flow or pressure fromexiting product tank 249 and entering first sieve bed 221. Similarly,second check valve 236 is disposed between second sieve bed 222 andproduct tank 249 and is configured to prevent flow or pressure fromexiting product tank 249 and entering second sieve bed 222.

In some embodiments, product gas supply stage 240 may further includeone or more of a tank pressure measurement device 241, a pressureregulator 242, a flow measurement device 243, an oxygen sensor 244, amanual flow-control device 245, such as an adjustable orifice, an outletfilter 246, and an accumulator tank 247, each disposed downstream ofproduct tank 249 as shown, or in any other configuration that issuitable for operation of oxygen concentrator 130 as described herein.Tank pressure measurement device 241 measures the current pressure inproduct tank 249 and transmits the measured pressure to controller 210.Pressure regulator 242 is disposed downstream of product tank 249, andis configured to regulate the higher product tank pressure down to atarget delivery pressure in a downstream portion of product gas supplystage 240. Thus, oxygen-enriched product gas 132 that is at the currentproduct tank pressure flows from a first conduit or other portion ofproduct gas supply stage 240, through pressure regulator 242, to enter asecond conduit or other portion of product gas supply stage 240 at thetarget delivery pressure. For example, one such target delivery pressuremay be a maximum inlet pressure that is recommended for proper operationof respiratory ventilation device 120. Flow measurement device 243measures flow of oxygen-enriched product gas 132 and transmits themeasured flow to controller 210, and oxygen sensor 244 measures thecurrent oxygen concentration of oxygen-enriched product gas 132 andtransmits the measured oxygen concentration to controller 210. Manualflow-control device 245 controls the continuous flow rate ofoxygen-enriched product gas 132 when oxygen concentrator 130 is coupledto ambient pressure delivery device 140. In some embodiments, manualflow-control device 245 includes an adjustable orifice, such as arotameter coupled to a needle valve. Outlet filter 246 removesparticulates from oxygen-enriched product gas 132 before delivery topatient 101.

Accumulator tank 247 is a storage vessel configured to store somequantity of oxygen-enriched product gas 132 during operation of oxygenconcentrator 130. As set forth above, when output 131 of oxygenconcentrator 130 is fluidly coupled to respiratory ventilation device120, accumulator tank 247 is configured to temporarily storeoxygen-enriched product gas 132 between each patient inspiratory effortand to supply the stored product gas at a consistent flow rate duringeach patient inspiratory effort. Consequently, product tank depletion inoxygen concentrator 130 can be prevented during the high product gasdemand that can occur during each patient inspiratory effort, therebyensuring that product gas is supplied to respiratory ventilation device120 at a consistent flow rate. Prevention of product tank depletion isdescribed in greater detail below in conjunction with FIG. 5. Bycontrast, when output 131 of oxygen concentrator 130 is fluidly coupledto ambient pressure delivery device 140, pressure in accumulator tank247 generally decays to approximately ambient pressure plus whateverpressure drop is associated with the flow of oxygen-enriched product gas132 to and through ambient pressure delivery device 140.

In some embodiments, accumulator tank 247 is configured as a constantvolume pressure vessel that stores oxygen-enriched product gas 132, suchas a metallic cylinder and the like. In such embodiments, volume demandfrom respiratory ventilation device 120 results in pressure drop inaccumulator tank 247 as oxygen-enriched product gas 132 exitsaccumulator tank 247 to satisfy the volume demand. In some embodiments,accumulator tank 247 is configured as a constant pressure/variablevolume storage vessel that maintains a constant or substantiallyconstant pressure therein even as oxygen-enriched product gas 132 exitsaccumulator tank 247. In one such embodiment, accumulator tank 247 isconfigured as a balloon accumulator that includes an elastic membrane oris formed from an elastic material. In another such embodiment,accumulator tank 247 is configured as a constant pressure cylinder orother pressure vessel with a movable piston that is driven by a springor pneumatic pressure to exert a substantially constant pressure on gasstored therein. The constant pressure cylinder can maintainsubstantially constant pressure on gas stored therein across a widerange of volumes, thereby providing a constant supply pressure torespiratory ventilation device 120.

Controller 250 is coupled to one or more of first sieve bed fill valve231, first sieve bed dump valve 232, second sieve bed fill valve 233,second sieve bed dump valve 234, and any sensors included in oxygenconcentrator 130. Controller 250 may be any suitable processorimplemented as a central processing unit (CPU), an application-specificintegrated circuit (ASIC), a field programmable gate array (FPGA), anyother type of processing unit, or a combination of different processingunits. In general, controller 250 may be any technically feasiblehardware unit capable of processing input signals or other data and/orexecuting software applications to facilitate operation of oxygenconcentrator 130 as described herein. Furthermore, in some embodiments,controller 250 may include a memory 251. Memory 251 may include volatilememory, such as a random access memory (RAM) module, and non-volatilememory, such as a flash memory unit, a read-only memory (ROM), or anyother type of memory unit or combination thereof suitable for use incontroller 250. In such embodiments, memory 251 is configured to storeany instructions, software programs, operating system, drivers, and thelike, that facilitate operation of controller 250 and any processorsmaking up controller 250.

In operation, oxygen concentrator 130 generates oxygen-enriched productgas 132 via a process that includes a fill phase for each of first sievebed 221 and second sieve bed 222, a dump phase for each of first sievebed 221 and second sieve bed 222, and an equalization phase. The fillphase for first sieve bed 221 occurs concurrently with the dump phasefor second sieve bed 222, while the fill phase for second sieve bed 222occurs concurrently with the dump phase for first sieve bed 221. Bycontrast, the equalization phase for first sieve bed 221 and theequalization phase for second sieve bed 221 occur simultaneously.

FIG. 3 is a graph illustrating pressure at various locations within aconventional oxygen concentrator while the oxygen concentrator isfluidly coupled to ambient pressure delivery device 140 and provides aconstant flow of oxygen-enriched gas, according to various embodimentsof the invention. Thus, the conventional oxygen concentrator delivers aconstant flow of an oxygen-enriched gas 132, for example to patient 101in FIG. 1. The conventional oxygen concentrator may be substantiallysimilar to oxygen concentrator 130, except without accumulator tank 247.The process by which the conventional oxygen concentrator provides theoxygen-enriched gas includes an equalization phase 301, a firstdump/fill phase 302, and a second dump/fill phase 303. A product tankpressure 321, a first sieve bed pressure 322, and a second sieve bedpressure 323 are all depicted over the course of equalization phase 301,first dump/fill phase 302, and second dump/fill phase 303. In addition,the actuations of first sieve bed fill valve 231 and second sieve bedfill valve 233 are shown. Also depicted in FIG. 3 are a first fill time302A, in which product tank 249 is filled from first sieve bed 221, anda second fill time 303A, in which product tank 249 is filled from secondsieve bed 222. It is noted that the filling phase for first sieve bed221 and the dump phase for second sieve bed 222 take place during firstdump/fill phase 302, while the fill phase for second sieve bed 222 andthe dump phase for first sieve bed 221 take place during seconddump/fill phase 303.

In the filling phase for first sieve bed 221 (i.e., first dump/fillphase 302), the output of pump 202, which is controlled by first sievebed fill valve 231 and second sieve bed fill valve 233, is directed tofirst sieve bed 221, in which nitrogen is removed and an oxygen-enrichedgas is formed. As a result, the pressure in first sieve bed 221increases as shown. When pressure in first sieve bed 221 increases to alevel equal to the pressure in product tank 249, first fill time 302Abegins. That is, first sieve bed pressure 322 is equal to product tankpressure 321, the corresponding check valve (i.e., first check valve235) opens, the oxygen-enriched gas in first sieve bed 221 entersproduct tank 249, and the pressure in product tank 249 increases inparallel with and equal to the pressure in first sieve bed 221, asshown.

The dump phase for second sieve bed 222 also occurs during firstdump/fill phase 302 (and concurrent with the above-described fillingphase for first sieve bed 221). In the dump phase for second sieve bed222, second sieve bed dump valve 234 is open to ambient, so thataccumulated nitrogen within second sieve bed 222 is dumped and thepressure in second sieve bed decreases as shown.

It is noted that, as pump 202 fills first sieve bed 221 and the pressuretherein exceeds the pressure in second sieve bed 222, a portion of theoxygen-enriched gas formed in first sieve bed 221 flows into secondsieve bed 222 via equalization orifice 223. As a result, the removal ofnitrogen from the second sieve bed 222, which is in the dump phase, isfacilitated. It is further noted that the rate at which the pressure offirst sieve bed 221 increases is a function of multiple factors,including, without limitation: the pump flow characteristics of pump202; the volume of first sieve bed 221; the size of equalization orifice223, and, once the pressure in first sieve bed 221 equals the pressurein product tank 249, the volume of product tank 249.

After the currently filling sieve bed, i.e., first sieve bed 221, issaturated with nitrogen or is approaching saturation, equalization phase301 is performed, i.e., the equalization phase 301 that occurs betweenfirst dump/fill phase 302 and second dump/fill phase 303. Equalizationphase 301 begins when first sieve bed fill valve 231 and second sievebed fill valve 233 open, while first sieve bed dump valve 232 and secondsieve bed dump valve 234 close. As a result, pressure in first sieve bed221 and second sieve bed 222 equalizes via equalization orifice 223, sothat the pressure in what was the filling sieve bed (i.e., first sievebed 221) is used to quickly increase pressure in what was thenon-filling sieve bed (i.e., second sieve bed 222). During thisequalization step 301, first sieve bed 221 and second sieve bed 222 bothreceive air from pump 202 without any exhausting of gases.

Upon completion of equalization phase 301, second dump/fill phase 303begins, in which first sieve bed 221 is exhausted to ambient via firstsieve bed dump valve 232, and second sieve bed 222 is filled via secondsieve bed fill valve 233. The above-described process then repeats andalternates between first sieve bed 221 and second sieve bed 222 tocyclically charge product tank 249 with an oxygen-enriched gas, such asoxygen-enriched product gas 132 in FIG. 1.

In sum, FIG. 3 depicts the pressure waveforms of first sieve bed 221,second sieve bed 222, and product tank 249 when the conventional oxygenconcentrator supplies a constant flow of oxygen-enriched gas via theabove-described PSA oxygen concentrator process. The saw tooth profileof product tank pressure 321 shows the increase of pressure of fillingfrom one of first sieve bed 221 and second sieve bed 222, and thesubsequent linear reduction in pressure during draining due to theconstant flow delivery of the oxygen-enriched gas from product tank 249.The rate of decay (slope) 305 in product tank pressure 321 when notfilling is a function of the volume of product tank 249 and the flowrate at which the oxygen-enriched gas is delivered from product tank249. For example, when such a flow rate is reduced, the slope 305becomes less negative.

It is noted that the increase in product tank pressure 321 continuesuntil a dump/fill phase ends, and the time duration of each dump/fillphase is generally set as a predetermined cycle time. Alternatively,controller 250 is configured to adjust the min-to-max range of producttank pressure 321 during operation for a particular product flow rate(i.e., slope 305) by adjusting a control output in the conventionaloxygen concentrator to modify operation of the conventional oxygenconcentrator. For example, controller 250 may adjust the timing of oneor more valves in the conventional oxygen concentrator, or may adjust anoutput of pump 202 in oxygen concentrator 130. Thus, the maximum producttank pressure 321 can be increased by controller 250, thereby increasingthe quantity of oxygen-enriched product gas 132 that is stored inproduct tank 249.

According to embodiments of the invention, the output of oxygenconcentrator 130, as shown in FIG. 1A, can be fluidly connected torespiratory ventilation device 120, which does not provide a constantflow of inhalation gas 123 to patient 101. Instead, respiratoryventilation device 120 provides inhalation gas 123 to patient 101intermittently, typically in response to an inspiratory effort bypatient 101. As a result, oxygen-enriched product gas 132 is deliveredfrom product tank 249 of oxygen concentrator 130 in intermittent pulses,rather than at a constant flow rate. Consequently, the pressurewaveforms of first sieve bed 221, second sieve bed 222, and product tank249 of oxygen concentrator 130 behave differently than depicted in FIG.3. Such behavior is illustrated in FIG. 4.

FIG. 4 is a graph illustrating pressure at various locations within aconventional oxygen concentrator while the oxygen concentrator providesan intermittent volume of oxygen-enriched gas to respiratory ventilationdevice 120. The conventional oxygen concentrator may be substantiallysimilar to oxygen concentrator 130, except without accumulator tank 247.The process by which such an oxygen concentrator providesoxygen-enriched product gas 132 may be substantially similar to by whichoxygen concentrator 130 delivers a constant flow, and includesequalization phase 301, first dump/fill phase 302, and second dump/fillphase 303. However, as shown in FIG. 4, in a spontaneous deliveryscenario, the pressure waveform behavior of product tank pressure 321can be significantly different than in the constant flow deliveryscenario illustrated in FIG. 3. In a spontaneous delivery scenario,respiratory ventilation device 120 spontaneously and intermittentlydelivers inhalation gas 123, which includes oxygen-enriched gas 132 fromproduct tank 249 of oxygen concentrator 120. In such a spontaneousdelivery scenario, the pressure waveform behavior of product tank 249includes constant pressure intervals 401 and pressure drops 402.

Constant pressure intervals 401, i.e., the horizontal segments ofproduct tank pressure 321, indicate that respiratory ventilation device120 is not delivering inhalation gas 123 to patient 101 at a time that asieve bed is not delivering oxygen-enriched gas to product tank 249.That is, the presence of a constant pressure interval 401 indicates thatrespiratory ventilation device 120 is not delivering inhalation gas 123to patient 101 either during equilibrium phase 301 or during a portion403 of a fill phase in which product tank pressure 321 is greater thaneither first sieve bed pressure 322 or second sieve bed pressure 323. Bycontrast, pressure decay slopes 405 result when respiratory ventilationdevice 120 spontaneously delivers inhalation gas 123 and a significantportion of the oxygen-enriched product gas 132 stored in product tank249 exits product tank 249, Pressure decay slope 405 is a function ofthe flow rate of oxygen-enriched gas 132 from the oxygen concentrator torespiratory ventilation device 120 and the volume of product tank 249.Furthermore, the magnitude of pressure drop 402 (which occurs during atime that a sieve bed is not delivering oxygen-enriched gas to producttank 249) is a function of the quantity of oxygen-enriched gas deliveredfrom the oxygen concentrator and the volume of product tank 249.

For clarity of description, in the embodiment of FIG. 4, the behavior ofthe pressure waveforms within the oxygen concentrator have beensimplified. Specifically, the frequency of patient respiration isassumed to be essentially equal to that of the frequency of thedump/fill cycle of product tank 247. As a result, a single pressuredecay slope 405 is shown for each dump/fill cycle of product tank 247.In practice, the phase and frequency of patient respiration isindependent of the phase and frequency of the product tank dump/fillcycle. Consequently, patient inhalation can occur at a time that causesa pressure decay slope 405 to occur when product tank pressure 321 isalready at a low pressure state 409, such as immediately before the mostrecently charged sieve bed has begun delivering oxygen-enriched productgas 132 to product tank 247. In such a scenario, the volume ofoxygen-enriched product gas 132 delivered to patient 101 by respiratoryventilation device 120 can cause product tank pressure 321 to drop belowthe target supply pressure of pressure regulator 242. When the pressurein the portion of product gas supply stage 240 that is downstream ofpressure regulator 242 falls below such a target delivery pressure, theflow rate of oxygen-enriched product gas 132 to respiratory ventilationdevice 120 generally drops below a target flow rate, and patient 101receives less oxygen-enriched product gas 132 than expected.

According to various embodiments, accumulator tank 247 is employed inoxygen concentrator 130 to prevent the above-described scenario in whichproduct tank depletion occurs. The presence of accumulator tank 247 inproduct gas supply stage 240 significantly modifies the pressure wavebehavior of product tank pressure 321, as described below in conjunctionwith FIG. 5 and FIG. 6.

FIG. 5 is a graph 500 illustrating pressure at various locations withinoxygen concentrator 130 as oxygen concentrator 130 provides anintermittent volume of oxygen-enriched gas to respiratory ventilationdevice 120, according to various embodiments of the invention.Specifically, graph 500 shows the pressure waveforms of first sieve bed221 (i.e., first sieve bed pressure 322), second sieve bed 222 (i.e.,second sieve bed pressure 323), and product tank 249 (i.e., product tankpressure 321). In addition, graph 500 shows the pressure waveform ofaccumulator tank 247 as accumulator tank pressure 501. It is noted thatthe embodiment of accumulator tank pressure 501 illustrated in FIG. 5 isfor a constant volume embodiment of accumulator tank 247, rather than aconstant pressure embodiment of accumulator tank 247.

As shown, accumulator tank pressure 501 varies over time in response toa volume demand from respiratory ventilation device 120, i.e., whenrespiratory ventilation device 120 spontaneously delivers inhalation gas123 to patient 101. During such delivery of inhalation gas 123 (whichincludes oxygen-enriched product gas 132 from oxygen concentrator 130),a portion of the oxygen-enriched product gas 132 stored in accumulatortank 247 exits accumulator tank 247, accumulator tank pressure 501drops, and additional oxygen-enriched product gas 132 stored in producttank 249 flows into accumulator tank 247. Consequently, even though asignificant volume of oxygen-enriched product gas 132 exits accumulatortank 247 during delivery of oxygen-enriched product gas 132 torespiratory ventilation device 120, accumulator tank pressure 501 onlydrops slightly, as indicated by pressure decay slopes 505. Further,because the volume demand from respiratory ventilation device 120 issatisfied with oxygen-enriched product gas 132 stored in accumulatortank 247, the only flow of oxygen-enriched product gas 132 from producttank 249 is at the constant flow rate determined by manual flow-controldevice 245. It is noted that the flow capacity of accumulator tank 247is generally significantly higher than the rate of flow allowed bymanual flow-control device 245.

Once delivery of inhalation gas 123 ceases, flow of oxygen-enrichedproduct gas 132 out of accumulation tank 247 also ceases, whileoxygen-enriched product gas 132 continues to flow into accumulator tank247. Consequently, accumulator tank pressure 501 increases with apressure rise slope 506 until another delivery of inhalation gas 123occurs, or until accumulator tank pressure 501 reaches the targetdelivery pressure of pressure regulator 242. The slope of pressure riseslope 506 is a function of multiple factors, including the volume ofaccumulator tank 247, the setting of manual flow-control device 245, thequantity of oxygen-enriched product gas 132 just delivered to patient101, and the target delivery pressure of setting of pressure regulator242.

The slope of pressure decay slope 506 is a function of multiple factors,including the volume of accumulator tank 247, the flow rate at which theoxygen-enriched product gas 132 is delivered from accumulator tank 247to respiratory ventilation device 120, and the rate at whichoxygen-enriched product gas 132 flows into accumulator tank 247 fromproduct tank 249. Thus, when accumulator tank 247 is sizedappropriately, a low-volume, constant flow demand is placed on producttank 249 during delivery of oxygen-enriched product gas 132 torespiratory ventilation device 120. As a result, product tank pressure321 shows similar behavior to that when oxygen concentrator 130 iscoupled to ambient pressure delivery device 140, and is shown in FIG. 5.Specifically, in such an embodiment, product tank pressure 321 includesno or very brief constant pressure intervals or steep pressure drops,such as constant pressure intervals 401 and pressure drops 402 in FIG.4. Instead, product tank pressure 321 shows the saw tooth profileassociated with the pressure increase during filling from one of firstsieve bed 221 and second sieve bed 222, and the subsequent linearreduction in product tank pressure during draining due to the constantflow delivery of the oxygen-enriched gas from product tank 249 toaccumulator tank 247.

In some embodiments, accumulator tank 247 can be sized to store aquantity of oxygen-enriched product gas 132 that is approximately equalto or greater than a typical volume of oxygen-enriched product gas 132that is expected to be delivered during a single patient respiratoryeffort. In such embodiments, accumulator tank pressure 501 may dropsignificantly, depending on the minimum inlet pressure of respiratoryventilation device 120. However, due to the presence of manualflow-control device 245 and pressure regulator 242 between accumulatortank 247 and product tank 249, the pressure swings experienced byaccumulator tank pressure 501 are generally not reflected in producttank pressure 321.

In embodiments in which the preferred supply/inlet pressure ofrespiratory ventilation device 120 falls within a relatively narrowpressure range, accumulator tank 247 can be sized to prevent unwantedpressure swing in the portion of product gas supply stage 240 proximateoutput 131 of oxygen concentrator 130. In such embodiments, accumulatortank 247 can be sized to have a sufficient storage volume (when at apeak pressure) to store a quantity of oxygen-enriched product gas 132that is at least about two times that of a typical volume ofoxygen-enriched product gas 132 that is expected to be delivered duringa single patient respiratory effort. In such embodiments, the peakpressure is typically equal to the target (i.e., downstream) pressure ofpressure regulator 242. Thus, once accumulator tank 247 reaches the peakpressure, a single delivery of oxygen-enriched product gas 132 topatient 101 can be mostly or entirely satisfied by accumulator tank 247.As a result, the pressure in the portion of product gas supply stage 240disposed between pressure regulator 242 and accumulator tank 247 willnot drop significantly below the target delivery pressure of pressureregulator 242, and product tank 249 will not undergo a steep pressuredecay.

FIG. 6 is a graph 600 illustrating pressure at various locations withinoxygen concentrator 130 as oxygen concentrator 130 provides a constantflow of oxygen-enriched gas to an ambient pressure delivery device 140,according to various embodiments of the invention. Specifically, graph600 shows the pressure waveforms of first sieve bed 221 (i.e., firstsieve bed pressure 322), second sieve bed 222 (i.e., second sieve bedpressure 323), and product tank 249 (i.e., product tank pressure 321).In addition, graph 600 shows the pressure waveform of accumulator tank247 as accumulator tank pressure 601. It is noted that the embodiment ofaccumulator tank pressure 601 illustrated in FIG. 6 is for a constantvolume embodiment of accumulator tank 247, rather than a constantpressure embodiment of accumulator tank 247.

As shown, accumulator tank pressure 601 remains constant and onlyslightly above ambient pressure. Specifically, accumulator tank pressure601 is a function of the flow rate as set by manual flow-control device245 and the pressure drop characteristics of ambient pressure deliverydevice 140 and tubing associated therewith. Furthermore, it is notedthat product tank pressure 321 includes no or very brief constantpressure intervals or steep pressure drops, such as constant pressureintervals 401 and pressure drops 402 in FIG. 4, and instead shows thesaw tooth profile associated with the pressure increase during fillingfrom one of first sieve bed 221 and second sieve bed 222, and thesubsequent linear reduction during draining due to the constant flowdelivery of the oxygen-enriched gas from product tank 249 to accumulatortank 24 y and patient 101. Thus, as illustrated by FIGS. 5 and 6, oxygenconcentrator 130 can operate effectively when providing oxygen-enrichedproduct gas 132 to either ambient pressure delivery device 140 orrespiratory ventilation device 120.

In sum, embodiments of the present invention provide an oxygenconcentrator that is configured for use in conjunction with a mechanicalventilator and an ambient pressure delivery device. Specifically, anaccumulator tank is disposed proximate the outlet of the oxygenconcentrator, so that some or all of the product gas supplied to themechanical ventilator during a period of volume demand is provided bythe accumulator tank, rather than a product tank of the oxygenaccumulator.

At least one advantage of the disclosed design is that pressure swingeffects are reduced or avoided in the product tank when the oxygenconcentrator is coupled to a mechanical ventilator. Thus, a moreconstant flow of product gas to the mechanical ventilator is providedrelative to prior art designs.

The descriptions of the various embodiments have been presented forpurposes of illustration, but are not intended to be exhaustive orlimited to the embodiments disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the described embodiments.

The invention has been described above with reference to specificembodiments. Persons of ordinary skill in the art, however, willunderstand that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. For example, and without limitation,although many of the descriptions herein refer to devices, personsskilled in the art will appreciate that the systems and techniquesdescribed herein are applicable to other types of devices. The foregoingdescription and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

What is claimed is:
 1. An apparatus, comprising: a product tank that isfluidly coupled to at least one sieve bed; a product gas accumulatortank that is fluidly coupled to the product tank via a first conduit andto an outlet port via a second conduit; and at least one controllerdisposed to control gas flow in the first conduit, wherein the firstconduit and the second conduit are disposed to allow at least a portionof product gas to flow from the product tank to the outlet port, and theapparatus is configured to produce a targeted spontaneous gas flow to arespiratory ventilation device, wherein the targeted spontaneous gasflow to the respiratory ventilation device is more than 20 liters perminute.
 2. The apparatus of claim 1, wherein the product tank is fluidlycoupled to the at least one sieve bed via a check valve that allows flowfrom the at least one sieve bed to the product tank.
 3. The apparatus ofclaim 1, further comprising a filter that is disposed inline in thefirst conduit, wherein the product gas accumulator tank is disposedbetween the filter and an outlet of the apparatus.
 4. The apparatus ofclaim 1, further comprising a flow control orifice that is disposedinline in the first conduit, wherein the product gas accumulator tank isdisposed between the flow control orifice and an outlet of theapparatus.
 5. The apparatus of claim 1, further comprising an oxygensensor that is disposed inline in the first conduit, wherein the productgas accumulator tank is disposed between the oxygen sensor and an outletof the apparatus.
 6. The apparatus of claim 1, further comprising apressure regulator that is disposed inline in the first conduit andregulates a pressure in a first portion of the first conduit down to atarget pressure in a second portion of the first conduit.
 7. Theapparatus of claim 6, wherein the second portion of the first conduit isfluidly coupled to the product gas accumulator tank.
 8. The apparatus ofclaim 1, wherein the product gas accumulator tank comprises a constantvolume pressure vessel.
 9. The apparatus of claim 1, wherein the productgas accumulator tank comprises a variable volume pressure vessel. 10.The apparatus of claim 9, wherein the variable volume pressure vesselcomprises one of a balloon accumulator or a movable piston thatmaintains a substantially constant pressure in the variable volumepressure vessel.
 11. A system, comprising: a respiratory ventilationdevice; and an oxygen concentrator with an outlet fluidly coupled to aninlet of the respiratory ventilation device, the oxygen concentratorcomprising: a product tank that is fluidly coupled to at least one sievebed, a product gas accumulator tank that is fluidly coupled to theproduct tank via a first conduit and to an outlet port via a secondconduit, and at least one controller disposed to control gas flow in thefirst conduit; wherein the first conduit and the second conduit aredisposed to allow at least a portion of product gas to flow from theproduct tank to the outlet port, and the system is configured to controlgas flow to produce a targeted spontaneous gas flow from the product gasaccumulator tank to the respiratory ventilation device, wherein thetargeted spontaneous gas flow to the respiratory ventilation device ismore than 20 liters per minute.
 12. The system of claim 11, wherein,when operating at peak pressure, the product gas accumulator tank has astorage volume sufficient to store a quantity of oxygen-enriched productgas that is equal to or greater than a quantity of oxygen-enrichedproduct gas associated with a single volume demand of the respiratoryventilation device.
 13. The system of claim 11, wherein the product tankis fluidly coupled to the at least one sieve bed via a check valve thatallows flow from the at least one sieve bed to the product tank.
 14. Thesystem of claim 11, further comprising a filter that is disposed inlinein the first conduit, wherein the product gas accumulator tank isdisposed between the filter and an outlet of the oxygen concentrator.15. The system of claim 11, further comprising a flow control orificethat is disposed inline in the first conduit, wherein the product gasaccumulator tank is disposed between the flow control orifice and anoutlet of the oxygen concentrator.
 16. The system of claim 11, furthercomprising an oxygen sensor that is disposed inline in the firstconduit, wherein the product gas accumulator tank is disposed betweenthe oxygen sensor and an outlet of the oxygen concentrator.
 17. Thesystem of claim 11, further comprising a pressure regulator that isdisposed inline in the first conduit and regulates a pressure in a firstportion of the first conduit down to a target pressure in a secondportion of the first conduit.
 18. The system of claim 17, wherein thesecond portion of the first conduit is fluidly coupled to the productgas accumulator tank.
 19. The system of claim 11, wherein the productgas accumulator tank comprises a constant volume pressure vessel. 20.The system of claim 11, wherein the product gas accumulator tankcomprises a variable volume pressure vessel.
 21. The apparatus of claim1 wherein: the respiratory ventilation device comprises an entrainmentelement, and a targeted spontaneous gas flow to a patient is more than100 liters per minute.
 22. The system of claim 11, wherein: therespiratory ventilation device comprises an entrainment element, and atargeted spontaneous pas flow to a patient is more than 100 liters perminute.